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Old 12th September 2016, 12:09   #61
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Default Re: Car A/C in fresh air mode?

Related question here: Sometimes, the outside temperature is perfect and there is no need for AC. However, when driving on the highway, I'd like to keep the windows shut to reduce wind noise.

I find that leaving the blower on (speed 2) and AC off in fresh air mode doesn't ventilate the car sufficiently. It gets stuffy after a while with three adults inside. Is this the case in most cars?
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Old 12th September 2016, 12:19   #62
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Default Re: Car A/C in fresh air mode?

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Originally Posted by McLaren Rulez View Post
Sometimes, the outside temperature is perfect and there is no need for AC. However, when driving on the highway, I'd like to keep the windows shut to reduce wind noise.

I find that leaving the blower on (speed 2) and AC off in fresh air mode doesn't ventilate the car sufficiently. It gets stuffy after a while with three adults inside. Is this the case in most cars?
Nice question!

The thing is, when you say the temperature outside is perfect, that is the ambient temperature in an open space.

However, the fresh air mode takes air from the vents at the bottom of the dashboard (see picture below) and feeds that in through the firewall into the car. Now, the air temperature in such a situation will be affected by localized temperature also - namely the heat soak that occurs in the engine compartment. With the motion of the car, that heat is moving closer to the firewall, and in turn raises the temperature of the inlet air just enough to take the comfort out of it.
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The second thing is, in a closed car, the perspiration of the occupants raises the humidity of the air. More than heat, it is humidity that causes discomfort since higher humidity prevents sweat from drying off and thereby cooling you. When the AC is running, it also dehumidifies the air, improving comfort levels. When the AC is off, this humidity has nowhere to go (it cannot just be ejected from the passenger compartment).

So, the gist of it is - keep the AC running - even if the temperature isn't set so you feel cooler, it will still dehumidify the air and improve comfort.
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Old 12th September 2016, 12:30   #63
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Default Re: Car A/C in fresh air mode?

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Originally Posted by arunphilip View Post
The second thing is, in a closed car, the perspiration of the occupants raises the humidity of the air. More than heat, it is humidity that causes discomfort since higher humidity prevents sweat from drying off and thereby cooling you. When the AC is running, it also dehumidifies the air, improving comfort levels. When the AC is off, this humidity has nowhere to go (it cannot just be ejected from the passenger compartment).
Good answer! Now that I think about it, I suspect the second point is the main contributor to the stuffy feeling. Guess the AC has to be on or the windows must be opened unless it is a lot colder outside.

Now that I think about it, those butterfly windows on some MPVs as well as those quarter-glass windows that could opened in older cars make so much sense! They help the air actually flow through and out of the car with minimal noise - precisely what one needs in this situation.

Last edited by McLaren Rulez : 12th September 2016 at 12:38.
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